A braid composed of multifilaments or monofilaments is used for various use applications such as fishing lines, blind cords and ropes. As a braid is diversified in use applications, the braid is required to have functionalities corresponding to the required characteristics of products. For example, when a braid is used for a fishing line, filaments made of synthetic fibers such as polyamide fibers, polyester fibers and polyolefin fibers and filaments made of fibers of metal such as stainless steel, tungsten metal and amorphous metal have been conventionally known as a general fishing line. A fishing line is required to have various characteristics depending on the kinds of fish for catching and fishing methods, and in general, thin fishing lines having high strength are desirable. Accordingly, braids composed of so-called ultra high molecular weight polyethylene fibers produced by a gel-spinning method are used for providing fishing lines having high strength and high elastic modulus (for example, see Patent Documents 1 and 2). The fishing lines made of ultra high molecular weight polyethylene fibers according to these inventions are fishing lines excellent in high strength and high elastic modulus, but have the problem that dimensional stability and physical characteristics fluctuate along with practical use and the lapse of time. For example, there is the problem that if such fishing lines are used as a fishing line product for a long term, the braided fibers are gradually fastened with the lapse of use time to lose ductility, which is an important factor for fishing lines, and gradual hardening of the fishing lines generates a dimensional change and accordingly causes fluctuation of physical properties. As means for solving the problem, there is disclosed a technique for producing a composite braid with other materials such as polyester monofilaments (for example, see Patent Document 3). Dimensional stability is increased by making a braid to be a composite braid, but use of commonly used polyester fibers leads to lowering of strength and elastic modulus. As other means for solving the problem, there is disclosed a technique for suppressing fluctuation of physical properties by, for example, performing a heat treatment after processing into a braid, but in this case, when a braid is used as a fishing line, there occurs not only the problem that the bundling property of fibers constituting the braid is weak so that the fibers braided are gradually fastened with the lapse of time, but also the problem that the cross sectional shape becomes so flat as to increase the friction with a fishing line guide and to lower wear resistance and throwing characteristics (for example, see Patent Document 4).
On the other hand, as blind cords to be used for blinds moving up and down, a braid has been conventionally used which is obtained by using a twisted yarn made of various kinds of synthetic fibers or natural fibers as a core yarn and coating the core yarn with a braided yarn made of various kinds of fibers, but along with enlargement of blinds, a conventional product cannot be satisfactory for use. Accordingly, it is strongly desired to produce cords more excellent in performance, particularly, in wear resistance. This kind of cord is used for blinds moving up and down, and therefore, it is important that not only dimensional change and untwisting are small even by repetitive use, but also transmissibility for moving up and down operation, that is, a stress at low strain is high. Further, it is also an important factor that fluctuation such as expansion and contract corresponding to change of environments including temperature and humidity is small for a long-term.
In the conventional techniques, there is not only the problem relevant to long-term use of a product but also the problem relevant to product storage. For example, there is the problem that physical properties which a product originally has fluctuate when the product is stored for a long-term in a warehouse without air conditioning equipment or is put in environments having large temperature fluctuation for a long-term such as inside a carrier for product transport or inside a ship container. The disclosed techniques described above cannot presently suppress dimensional change and fluctuation of physical properties with the lapse of time not only during use of a product but also during product storage.